1. Field of the Invention
This invention relates to vehicles having deployable passenger restraints, such as front air bags, seat-mounted air bags, door-mounted air bags, and side air curtains, that are concealed by synthetic trim covers through which the restraints are deployed in consequence of a condition, such as a crash, calling for restraint deployment. Forces exerted on the trim covers by restraint deployments fracture the trim covers along lines of weakness to create openings through which the restraints are deployed. This invention is particularly concerned with improvements for containment of fragments of fractured trim covers during deployment of the restraints through the trim covers, so that the fragments are not scattered into the interior of the passenger compartment.
2. Background Information
The state of the art is reflected by U.S. Pat. Nos. 5,372,379; 5,480,939; 5,863,064; 6,079,732; 6,142,506; 6,168,186; 6,179,324; 6,234,515; and 6,328,333 that were developed during a preliminary novelty search and that disclose various forms of trim covers through which various forms of deployable passenger restraints are deployed in motor vehicle crash situations. It is known to fabricate such trim covers from synthetic materials using known processes, such as plastic molding. It is also known to fabricate such trim covers with lines of weakness along which they will fracture as a result of restraint deployment forces acting on them as the restraints are being deployed through them.
Because such trim covers are disposed within the interiors of the passenger compartments of motor vehicles that are potentially subjected to a range of temperature extremes, it is desirable that the physical characteristics of the synthetic materials used in their manufacture be as stable as possible when subjected to environments where temperatures can range from polar cold to tropical desert heat. Certain known materials that possess such characteristics may be prohibitively costly for such use in an industry where piece cost is always a consideration in choosing a final design. Hence, the use of less costly synthetic materials is preferred, but not at the expense of compromising desired functionality.
One concern with some materials is that they may become brittle at very cold temperatures, such as ones approaching −40° C. At such temperatures, portions of a trim cover made of such a material may fragment as the trim cover is being fractured by a deploying air bag, and such fragmentation is generally considered unacceptable. Consequently, a known solution for resisting cold-temperature fragmentation comprises placing an electric heater element in proximity to the trim cover to keep its temperature above those where it might otherwise become prone to fragmentation upon fracture. In addition to its heater elements, that solution of course involves added electric circuits that must draw power from the vehicle electrical system. It would be better if such complications could be avoided.
Another solution previously proposed to avoid cold temperature embrittlement of a trim cover comprises fabricating the trim cover of a synthetic material, such as an impact-modified TPO and polyether-ester. While that material possesses desirable cold temperature properties, it tends to lose strength and dimensional stability at hot temperatures, such as ones approaching 70° C. and consequently may be poorly suited for certain trim cover applications.
The phrase “trim cover”, or “trim panel”, is being used here in a generic sense to include various parts that may be present within the interior of the passenger compartment of a motor vehicle. Some examples are “A”-pillar covers, “B”-pillar covers, roof rail covers, and instrument and dashboard panels, seat back side covers, and door trim panels.
In view of the state of the art, an improvement that would allow a trim cover to be fabricated in a cost-efficient manner using cost-efficient synthetic material, that would not require added accessory devices in the vehicle, such as electric heaters and associated electric wiring, and that would resist separation of fragments created as a result of deployment-induced fracture would seem quite desirable for the automotive industry.